Information may be secured in a number of ways. Information that is confidential in nature may comprise financial, medical, corporate, political or personal information, for example.
Confidential information may be stored in secure premises, preventing accidental or malicious access to the information by placing it in a locked place, such as for example in a safe in an office. Corporate locations may be further, or alternatively, provided with alarm systems, guards, fences and/or other access control functions.
Confidential information may be stored in computers that are not connected to any unsecure networks, to prevent unauthorized network intrusion therein to obtain the information. Such computers may be referred to as “air walled” computers as they have no connection to unsecure networks.
One way to prevent unauthorized access to confidential information is encryption, wherein a plaintext, for example a text in a natural language, such as French, is converted to a ciphertext using an encryption algorithm and a key. Encryption algorithms are designed to render it very difficult to obtain the plaintext from the ciphertext without the key. In general, ciphertext may be known as encrypted information.
In quantum communication, QC, two parties may exchange information encoded in quantum states. The quantum states may be qubits, which are composed of the superposition of two orthogonal states such as orthogonal polarization states of a photon or qubits, may comprise specially defined properties of photons such as pairs of polarization states, such as 0° and 90°. Diagonal, 45°, anti-diagonal, −45°, or circular basis states such as left-handedness and right-handedness are possible superpositions of the 0° and 90° polarization states. Through quantum communication, the two parties may produce a shared random series of bits known only to them, which can then be used as secret keys in subsequent encryption and decryption of messages. A third party can, in theory, eavesdrop on the QC between the two parties. Such eavesdropping perturbs the QC, however, introducing anomalies that the two intended parties can detect. The two parties may post-process the results of the QC to remove any partial information acquired by an eavesdropper, and form shared secret keys from the remaining information resulting from the QC.
An eavesdropper intercepting and re-transmitting a photon comprised in a quantum communication can only guess the original sending basis when it re-encodes and re-transmits the photon toward its original destination. The receiver may detect the eavesdropping since for subsets of bit values for which sending basis and measuring basis are found to match, parity values should match exactly, assuming the communication system is well tuned and free from imperfections in transmission and reception. Discrepancies in bit values introduced by eavesdropping enable the transmitter and receiver to detect eavesdropping and correct the secret keys.